Solid electrolytic capacitors (e.g., tantalum capacitors) have been a major contributor to the miniaturization of electronic circuits and have made possible the application of such circuits in extreme environments. Conventional solid electrolytic capacitors are often formed by pressing a metal powder (e.g., tantalum) around a metal lead wire, sintering the pressed part, anodizing the sintered anode, and thereafter applying a solid electrolyte. The solid electrolyte layer may be formed from a conductive polymer (e.g., poly(3,4-ethylenedioxythiophene)), such as described in U.S. Pat. Nos. 5,457,862 to Sakata, et al., 5,473,503 to Sakata, et al., 5,729,428 to Sakata, et al., and 5,812,367 to Kudoh, et al. The conductive polymer electrolyte of these capacitors has traditionally been formed through sequential dipping into separate solutions containing the ingredients of the polymer layer. For example, the monomer used to form the conductive polymer is often applied in one solution, while the catalyst and dopant is applied in a separate solution or solutions. One problem with this technique, however, is that it is often difficult and costly to achieve a relatively thick solid electrolyte, which is helpful for achieving good mechanical robustness and electrical performance. Also, such polymers can also delaminate from the part during encapsulation of the capacitor, which adversely impacts electrical performance. Various attempts have been made to address this problem. U.S. Pat. No. 6,987,663 to Merker, et al., for instance, describes the use of a polymeric outer layer that covers a surface of the solid electrolyte. Unfortunately, this technique is still problematic in that it is difficult to achieve good adhesion of the polymeric outer layer to the graphite/silver layer often used in terminating the solid electrolyte capacitor. Further, it is difficult to disperse such polymeric layers in aqueous mediums, which is desired in certain applications.
As such, a need remains for a solid electrolytic capacitor that possesses good mechanical robustness and electrical performance.